Oil change frequency

[super9064]

I posted this as a response on the Bird, thought I would share.
I hate to even post this, I know I'm going to get flamed, but here gos' My step father "Actual Rocket scientist" worked for a engineering company, a very prestigious engineering company. We once had a conversation about oil change frequency. He told me that they once received a contract from the Army, that requested they determine wear rates of engines that had their oil changed at various intervals to determine how often the oil really needed to be changed. The Army has 100s of 1000s of vehicles to maintain, and wanted to do a cost benefit analysis to see if it was worthwhile to change the oil more or less frequently.
The test consisted of running about a dozen motors for months on end. Each motor had a different oil change frequency, 3K, 6K, 10K etc. and a base line motor that only had fresh oil added to it as it was used up.
At the end of the test the engines were torn down and measured for wear, the motor that had the oil just added to it, as needed, had no more wear than the motor with the most frequent oil changes.
Reality check, the people and company's that advocate frequent oil changes, all have a interest $$$ in you changing oil more frequently, oil company's, car dealers, mechanics. That said, I change the oil as recommended by the manufacture, but I've always remembered that conversation, and don't stress out if I don't get the oil changed exactly when the time comes due.

[jeff eelkema]

An important point to consider is the type of usage. It has been published in many mechanical repair/engineering text books that the majority of engine wear occurs prior to the engine reaches full temp. While an engine warms the rings don't seal properly - everything is designed to be at the right clearance when all the different metals have expanded the correct amount - and as a result the oil gets contaminated by combustion gases and unburnt fuel from the rich mixture needed to maintain driveability.

Long haul trucks with constant speed, constant load, low revs and operating at normal temp for long periods can run long oil change intervals and get huge milage from the engine. A high reving, high output engine sports car engine will always wear more quickly. Engines doing short stop/start runs will form sludge. Engines that don't get regular oil changes will also form sludge. Left unchecked, this sludge often results in internal oil blockages and lubrication failure.

I don't have any interests in the oil industry and use my mechanical training as a consumer advocate. There is an old mechanics saying, oil is cheap, engines aren't!